The present invention relates to colored thermostable and lightfast dichroic polarizers based on water-soluble organic dyestuffs with sulfonic groups, and to processes of preparation thereof.
There exist dichroic polarizers produced by application of a true solution of a dichroic material on a substrate surface, solvent evaporation from the surface while at the same time bringing the material into the nematic phase, subjecting the material molecules to orienting influence and to mild solidifying influence to cause the material to be solidified in the oriented state. See U.S. Pat. Nos. 2,400,877 and 2,544,659. The dichroic nematic materials are water- and alcohol-soluble organic dyestuffs which enter the nematic state on the substrate surface immediately.
Dichroic polarizers from the above materials consist of a thin film of molecularly oriented dyestuff applied on a support surface. Such a film of dyestuff may be considered as a "polarizing coating". This term is used hereinbelow. In-service characteristics of polarizing coatings depend mainly on the dyestuffs' properties in contrast to dichroic polarizers based on stretched polymeric films mass-dyed with organic dyestuffs. See U.S. Pat. Nos. 5,007,942 and 5,059,356. The characteristics of the latter polarizers depend also on the polymer base properties.
According to aforementioned U.S. Pat. Nos. 2,400,877 and 2,544,659 the dyestuff solution is applied on a surface to which anisotropy was preliminarily imparted by mechanical rubbing. The orientation of dyestuff molecules takes place under influence of surface anisotropy when the solution is transferred through the nematic liquid crystalline state. This transfer is carried out directly on the support surface under solvent evaporation. Specific conditions must be satisfied to prevent disorientation of the dye molecules.
Known dichroic polarizers based on polarizing coatings have the following disadvantages:
1) these dichroic polarizers have low polarizing characteristics because these polarizers are based on dyestuffs which exist in the nematic liquid-crystalline phase a limited time only. This, together with a high viscosity of such a phase, does not allow ordering the dyestuff molecules in an effective manner; PA1 2) the dichroic polarizers have low lightfastness and heat resistance; PA1 3) the manufacturing process does not combine the orienting influence and application of dyes to the surface into one stage to be performed at the same time; PA1 4) the dichroic polarizers cannot be prepared without an external orienting influence by, for example, rubbing or electric or magnetic field. PA1 R.sup.1 =H, Cl; PA1 R=H, Alk, ArNH, or ArCONH; PA1 Alk is an alkyl group; PA1 Ar is a substituted or unsubstituted aryl radical; PA1 M is H.sup.+, a metal of the first group, or NH.sub.4.sup.+. ##STR2## ##STR3## PA1 R is H, an alkyl group, a halogen, or an alkoxy group; PA1 Ar is a substituted or unsubstituted aryl radical; PA1 n=2-3; PA1 M is as in formula I above. ##STR4##